Frost Dates, Onion Maggots, and Damping-Off.

April 4, 2019

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In this issue:

Frost

Onion Maggots

Damping-Off

FROST

Frost damage on spinach

Pepper deformity due to cold temperatures

Cold injury on a tomato

Overview

Timing is critical when deciding to plant your gardens or fields. Low temperatures and frost damage can reduce a plant’s growth and rate of metabolism. A vegetable crop’s hardiness will depend on its variety and genetics.

Damage

Damage to vegetables occurs when the water in and between the cells freezes and expands causing them to burst. This can cause the plant to appear dark green or water-soaked before turning dark and necrotic. Some vegetables such as collards, kale, lettuce, onions, potatoes, spinach, and turnips are most frost hardy as their leaves and roots are more capable to withstand the internal ice-formations. Vegetables that are less susceptible include cucumbers, eggplants, peppers, squashes, sweet corn, and tomatoes.

ONION MAGGOTS (Delia antiqua)

Overview

Adult onion maggot flies emerge from their overwintering sites in late April through May. They can go through one generation in about 3-4 weeks, totaling 2-3 generations per year.

Damage

The first generation is usually the most damaging as the larvae will feed on the roots and bulbs of the young onion. This ultimately causes wilting and plant death. A single larva can kill multiple onion seedlings during its growth and development. Later generations tend to be less severe, but the feeding can leave the bulb prone to rotting diseases and reduced quality and storability.

Management

Begin monitoring for populations by setting up yellow sticky cards in mid-May. (First generation usually has peak flights at the end of May)

Dispose of cull onions and onion debris by dumping or composting then covering with at least 12 inches of onion-free soil.

Remove and destroy volunteer onions in the spring.

Remove onion culls and debris from fields after harvest then till in the fall.

Rotate onion crops every season with unrelated crops.

Delay planting where onion maggots have been a problem in seasons prior.

DAMPING-OFF

Overview

Damping-off is a fungal disease caused by various soil pathogens such as Pythium, Rhizoctonia, Fusarium, and Phytophthora. It is most common in cold + wet soil that has poor drainage. Damping-off can occur both in the field and in the greenhouse. Damping-off is more likely to be present in unsanitary spaces, such as greenhouses with dirty benches or unsterile containers and equipment.

Damage

Symptoms of damping-off include mushy seeds that darken and decay, shriveled seedlings, or seedlings with weakened stems that topple over due to rotting.

Management

Sanitation is the most effective control strategy to manage damping-off. Ensure your greenhouse, growing area, and supplies are disinfected. Use new trays and pots every season. Make sure the sourced growing media is sterile and pathogen free.

If an infection is identified, seedlings should be disposed of immediately along with potentially infected seedlings nearby.